9.3 Add and Subtract Decimals

Three steps for adding or subtracting fractions
1. Make sure denominators are the same. (use LCM to find common denominator)
2. Add the numerators – write the sum over the common denominator
3. Simplify if necessary (this could mean writing as a mixed number).


How to Add & Subtract Fractions -- powered by eHow.com
Check out these examples from mathisfun.com

9.1 Estimate Sums and Differences (p.200-203)

I.Use benchmark numbers to estimate:
A. Benchmark numbers are numbers that are easy to work with --> 0, 1/2, 1 whole
B.Compare the numerator (top) to the denominator (bottom)

Find out if the numerator is:

• far away from the denominator (ex. 1/9: between 0 and 1/2, but closer to 0--> 0)


• close to half of the denominator (ex. 3/5: between 1/2 and 1, but closer to 1/2--> 1/2)


• almost the same as the denominator (ex. 7/8: it is between 1/2 and 1, but closer to 1--> 1 whole )

II. Use a range to estimate when you are working with quarters (equivalent to fourths)

A. 1/4 is exactly in the middle between 0 and 1/2 so we can use either 0 or 1/2 as estimates for 1/4.

ex. 3 1/4 + 2 7/8

3 1/4--> could be 3 or 3 1/2 for our estimate - use both to find the range

2 7/8 would become 3 for our estimate

3+3 = 6

3 1/2 + 3 = 6 1/2

The range is between 6 and 6 1/2, our estimate could 6 1/4 which is between 6 and 6 1/2

Chapter 9 Overview

Chapter 9 is a focus on adding and subtracting fractions. Here is a link from themathpage.com that explains most of the concepts we will be covering in Chapter 9.

8.5 Fractions, Decimals, and Percents (p.191-193)

I. Types of Decimals
A. Terminating Decimal: A fraction in decimal form that has zero has a remainder when you divide using long division.
ex: 1/2 = 0.5 = 0.50000000 (if you would try to keep dividing you would only get 00000... because there is nothing left to divide out)
B. Repeating Decimal A decimal that has a pattern of repeating numbers (or one number)- shown as a remainder when dividing--> use a horizontal line above repeating digits (called a vinculum)
ex: 1/9 = 0.1.... = 0.1
4/11 = 0.363636363636 = 0.36
**Try turning some of these fractions into decimal to find repeating patterns:
2/3
7/12
1/7
1/81

II. Turning common fractions into decimals
A. Divide the top number by the bottom number
Ex. 4/5 = 4÷ 5 = 0.8

III. Decimals into fractions
A. Decimals can be turned into percentages by moving the decimal point two places to the right (the the hundredths place)- this shows the value out of 100 equal parts (per cent=>per 100) making up the whole.
Ex: 1/4 = 1 ÷ 4 = 0.25 = 25%
Ex2: 1/3 = 1 ÷ 3 = 0.33...repeating = 33.3% (there should be a line over the 3 in the tenths place.

Try this activity from mathgoodies.com to see what you know
Here is an explanation from mathgoodies that might help too.